Rectangular or box-shaped ducts are extensively utilized in heating and ventilating systems to distribute heated or cooled air throughout a structure. These ducts are commonly formed from differing gauges of sheet metal in sections of predetermined lengths which are then connected to one another to form a continuous duct for distributing air.
Typically, each section of duct is formed by bending two pieces of sheet metal of the desired length at a 90° angle. One edge of each piece is formed to include a longitudinally extending groove, forming thereby the female portion of the seam, while the other longitudinal edge of each piece is bent over along its length to form thereby the male portion of the seam. The two pieces are then assembled by inserting the male portion of each piece into the female portion, leaving an edge extending beyond the joint from the female portion. This extended edge must then be bent over to lock the seam. This seam is known in the industry as a ‘Pittsburgh’ lock or seam.
While these known duct systems are successful to a degree, they suffer from several logistical problems. Firstly, the insertion of the male portion into the female portion of the seam requires a great deal of force due to the tight dimensional constraints of the formed female end. To accomplish this goal, operators must force the male end into the female end, typically utilizing a hammer or the like. Likewise, the extended edge of the female portion must also be hammered over in order to lock the seam closed. These hammering operations are highly labor intensive and quite loud, oftentimes requiring ear protection for the operators who assemble the finished duct work. Moreover, the time and effort extended on hammering the male portion into the female portion, and then hammering the extended edge of the female portion over to seal the seam, can substantially increase the time and expense of any duct fabrication and installation job, typically by as much as 50% or more.
With the forgoing problems and concerns in mind, it is the general object of the present invention to provide a duct fastseam which overcomes the above-described drawbacks while maximizing effectiveness and flexibility in the assembling process.